Use tap size as default size for scrolling start. reset IsGestureRecognitionSkipped when pointer is released

[emmauss]

What does the pull request do?

Sets the default ScrollStartDistance to the Platform settings' TapSize. Resets Pointer.IsGestureRecognitionSkipped of a pointer when pointer is released.

What is the current behavior?

The default value for ScrollStartDistance was 30. This is too large to detect for scrolling on most touch devices, and in some cases, controls maye be smaller than 30 and thus will force the scroll gesture recognizer to lose the pointer as the gesture may go over another control before it start to trigger scrolling.

What is the updated/expected behavior with this PR?

How was the solution implemented (if it's not obvious)?

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

Breaking changes

Obsoletions / Deprecations

Fixed issues

Fixes #15288

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0047794-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[workgroupengineering]

Suggested change

	private int _scrollStartDistance = (int)((AvaloniaLocator.Current?.GetService<IPlatformSettings>()?.GetTapSize(PointerType.Touch).Height ?? 10) / 2);
	private readonly static int s_defatultScrollStartDistance = ((AvaloniaLocator.Current?.GetService<IPlatformSettings>()?.GetTapSize(PointerType.Touch).Height ?? 10) / 2);
	private int _scrollStartDistance = s_defatultScrollStartDistance;

[emmauss]

Done

[workgroupengineering]

Why is it different form _scrollStartDistance?

Avalonia/src/Avalonia.Base/Input/GestureRecognizers/ScrollGestureRecognizer.cs

Line 17 in e9e383d

private int _scrollStartDistance = (int)((AvaloniaLocator.Current?.GetService<IPlatformSettings>()?.GetTapSize(PointerType.Touch).Height ?? 10) / 2);

[emmauss]

It's been changed to match.

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0047808-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[Meloman19]

I think it's better to initialize in the constructor (not static). IPlatfromSettings may be registered later than the initialization of a static variable and the value will be irrelevant.

Or even better, read out this parameter every time before use to take the current value. Because it can change.

Something like that.

// ScrollStartDistance is nullable. Because it will be used as a custom value.
private int? _scrollStartDistance = null;

// Add local field
private Size _pointerScrollStartDistance;

public static readonly DirectProperty<ScrollGestureRecognizer, int?> ScrollStartDistanceProperty =
            AvaloniaProperty.RegisterDirect<ScrollGestureRecognizer, int?>(nameof(ScrollStartDistance),
                o => o.ScrollStartDistance, (o, v) => o.ScrollStartDistance = v,
                unsetValue: null);

public int? ScrollStartDistance
{
    get => _scrollStartDistance;
    set => SetAndRaise(ScrollStartDistanceProperty, ref _scrollStartDistance, value);
}

protected override void PointerPressed(PointerPressedEventArgs e)
{
    if (e.Pointer.Type == PointerType.Touch || e.Pointer.Type == PointerType.Pen)
    {
        // ...
        // Init pointerScrollStartDistance on each recognize start
        // First, we check custom ScrollStartDistance. If it is set, then we use it.
        // Or use PlatformSettings depend on pointer type, or some default value
        _pointerScrollStartDistance = ScrollStartDistance != null
            ? new Size(ScrollStartDistance.Value, ScrollStartDistance.Value) 
            : ((AvaloniaLocator.Current.GetService<IPlatformSettings>()?.GetTapSize(e.Pointer.Type) / 2) ?? new Size(10, 10));
    }
}

protected override void PointerMoved(PointerEventArgs e)
{
    if (e.Pointer == _tracking)
    {
        var rootPoint = e.GetPosition(_rootTarget);
        if (!_scrolling)
        {
            // The vertical and horizontal values may differ, so we check them separately.
            // Width for X axis
            if (CanHorizontallyScroll && Math.Abs(_trackedRootPoint.X - rootPoint.X) > _pointerScrollStartDistance.Width)
                _scrolling = true;
            // Height for Y axis
            if (CanVerticallyScroll && Math.Abs(_trackedRootPoint.Y - rootPoint.Y) > _pointerScrollStartDistance.Height)
                _scrolling = true;
            if (_scrolling)
            {
                _trackedRootPoint = new Point(
                    _trackedRootPoint.X - (_trackedRootPoint.X >= rootPoint.X ? _pointerScrollStartDistance.Width : -_pointerScrollStartDistance.Width),
                    _trackedRootPoint.Y - (_trackedRootPoint.Y >= rootPoint.Y ? _pointerScrollStartDistance.Height : -_pointerScrollStartDistance.Height));

                Capture(e.Pointer);
            }
        }

        // ...
    }
}

[robloo]

spelling s_defatultScrollStartDistance default is wrong.

[emmauss]

Fixed

[emmauss]

I think it's better to initialize in the constructor (not static). IPlatfromSettings may be registered later than the initialization of a static variable and the value will be irrelevant.

Or even better, read out this parameter every time before use to take the current value. Because it can change.
Something like that.

IPlatformSettings is not expected to be changed during runtime. Also, changing the value to a nullable int will be a breaking change at this point.

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0047859-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[maxkatz6]

IPlatformSettings isn't expected to be changed, correct. It's not a service re-definable by user either. And we don't guarantee Avalonia types usable before initialization.

But in general, it's a good point for property default value factories: #5315